Heady discoveries

The yeast that gave rise to lager is tracked down to South America

IN THE 15th century a schism opened in the world of beer. Brewers in Bavaria alighted on a new version of that age-old drink—one that liked to be fermented in the cold and could thus be brewed in winter. The lager revolution had begun.

The difference between lagers and more traditional ales lies in the yeast. Ales are made with baker's yeast, Saccharomyces cerevisiae. Lagers use a hybrid, half cerevisiae and half something else. The interloper, though, has never been found—until now.

After a worldwide search, a team of geneticists has pinned it down to South America. Chris Todd Hittinger of the University of Wisconsin-Madison and Diego Libkind of the Argentine National Council for Scientific and Technical Research, found their quarry over 11,000km (7,000 miles) from Bavaria, in the cool alpine forests of Patagonia. As they explain in a paper in the Proceedings of the National Academy of Sciences, the newly described species, named Saccharomyces eubayanus, lives in galls that infect beech trees there. These sugary galls often ferment on the forest floor, and locals have been known to make an alcoholic beverage from them. Genetic sequencing confirmed that the yeast in the galls is 99.5% identical with the non-ale half of the lager-yeast genome.

That solves one mystery but creates another. Human transport is the only way the fungus could have travelled from Patagonia to Europe, but exploration of the New World did not begin until the end of the 15th century, and Patagonia was not reached until the 16th. Yet there are records of cold-fermented beer being made in Munich as early as 1420.

Dr Hittinger suspects lagering in its basic form—lengthy and cool fermentation—did precede the arrival of eubayanus, but that these early lagers were poor. Then, in one batch, eubayanus drifted in and could thrive at the low temperatures which cerevisiae disliked. Brewers favoured that batch, and the yeast spread. Indeed, the historical record provides a hint that something was afoot around this time. In 1553 Bavaria outlawed summer-made beer because wintertime brews had outstripped them in quality.

Eventually, the two yeast strains hybridised to form Saccharomyces pastorianus, the yeast used by lager brewers today. Those brewers will cheer the discovery of eubayanus, as it opens a trove of genes that did not make the transition to pastorianus but which might help the process of cold brewing. One South American beer company is already discussing using pure eubayanus, as well as lab-created hybrids, in a test brew. Whether that will improve the lager's flavour is another matter. As Dr Hittinger points out, natural selection has done a pretty tasty job already.